MIPS: Implement IC support for Constant Function transitions.

Port r15124 (6b02a945)

BUG=

Review URL: https://codereview.chromium.org/16984002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15133 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
MIPS: Only extend storage if FIELD

Port r15125 (0c202ff0)

BUG=

Review URL: https://codereview.chromium.org/16983002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15134 ce2b1a6d-e550-0410-aec6-3dcde31c8c00